The present invention relates to electrical medical leads generally; and, more particularly, relates to implantable cardiac pacing and defibrillation leads that include expandable electrodes.
Over the years, numerous leads have been designed for the purpose of pacing the atria. One basic approach has been to provide the lead with a pre-formed xe2x80x9cJxe2x80x9d-shape, adapted to result in the electrode at the tip of the lead being reliably located in the right atrial appendage. Various approaches to providing a J-shaped lead have included the provision of molded, curved polyurethane lead bodies or sheaths as in U.S. Pat. No. 4,394,866 issued to Hughes and U.S. Pat. No. 4,627,439 issued to Harris, curved silicone rubber sheaths as in U.S. Pat. No. 4,402,328 issued to Doring, curved coils as in U.S. Pat. No. 4,402,330 issued to Lindemans, and curved reinforcing wires as in U.S. Pat. No. 4,454,888 issued to Gold. Such curve providing structures are incorporated in the distal portion of the lead so that it maintains a J-shaped configuration after implant, allowing the electrode to continue to resiliently engage the right atrial appendage until such time as it is anchored in place by means of fibrotic tissue growth.
Pacing the atria has also been accomplished by means of electrode leads located in the coronary sinus. One of the earlier coronary sinus leads is the Medtronic, Inc. Model 6992 Coronary Sinus Lead which has a generally straight lead body, carrying two ring electrodes. More recently, leads having pre-formed curved configurations have been employed for pacing and/or mapping the electrical activity of the atria, including U.S. Pat. No. 5,423,772 issued to Lurie, U.S. Pat. No. 5,387,233 issued to Alferness et al., and pending, commonly assigned U.S. Pat. No. 5,683,445 to Swoyer, incorporated herein by reference in its entirety. An additional design for a curved coronary sinus lead is disclosed in commonly assigned U.S. Pat. No. 6,144,882 to Sommer et al., also incorporated herein by reference in its entirety.
One mechanism for retaining an electrode at a desired site of implant involves use of a compression mechanism that allows the electrode to be compressed during delivery, then expanded to contact the walls of a vessel. U.S. Pat. No. 5,071,407 to Termin et al. discloses a fixation element constructed of braided, helically wound filaments that are deformed during delivery. The filaments expand to form a cylindrical structure having a radius sized to contact surrounding tissue. Similar mechanisms are disclosed in U.S. Pat. Nos. 5,224,491 and 5,170,802 to Mehra, both of which disclose an electrode having a hollow, cylindrical conductive body inserted into the vessel in which the electrode is to be located and which is expanded into contact with the interior surface of the blood vessel.
Although the prior art discloses expandable members adapted to contact tissue for purposes of delivering electrical stimulation to the heart, the problem of orienting a discrete electrode associated with an expandable member has not been addressed. The orientation of a stimulating electrode may be critical in certain instances. For example, an electrode located in a coronary vein for pacing the atrium or the left ventricle may unintentionally stimulate nerves, causing patient discomfort. One known problem is the stimulation of the phrenic nerve by a pacing electrode placed in a posterior lateral vein. To prevent this stimulation from occurring, the surface of an electrode should be oriented toward, and make intimate contact with, the epicardial surface of the heart. The problem can be further reduced by ensuring that the surface area of the electrode is appropriate for the intended use. A large electrode surface not only wastes energy, but also increases the likelihood that unwanted nervous stimulation may occur.
What is needed, therefore, is an improved electrode assembly that may be oriented within the vasculature so that stimulation is directed to a predetermined target location, and unwanted stimulation is avoided.
The present invention includes an elastically compressible member at a distal end of a lead. During the implantation process, the compressible member is in a contracted state. After being delivered to the implant site and deployed, the compressible member expands, and is positively affixed within a cardiac vein or coronary artery. Compressible member includes at least one electrode that is urged into contact with tissue when the compressible member expands. Compressible member further includes a keyed structure designed to engage a stiffening member. The stiffening member is used both to deliver the compressible member to the implant site, and to rotate the compressible member, if necessary, so that the electrode contacts predetermined body tissue, and undesirable stimulation of muscle or other tissue is avoided.
In one embodiment, compressible member includes a conductor wound to form multiple turns. When the compressible member is deployed, stiffening member engages compressible member to cause all of the multiple turns to be substantially aligned. After deployment, however, at least one of the multiple turns moves out of alignment with other ones of the multiple turns so that compressible member has an enlarged profile sized to contact the walls of a cardiac vein or coronary artery.
In another embodiment, compressible member includes a spring clip that has a compressed profile during delivery, and an expanded profile after deployment. The spring clip defines an inner region, which in one embodiment, retains a flexible membrane-like structure adapted to prevent tissue in-growth to the spring clip.
In each of the embodiments, the electrode assemblies contain spring members that can be elastically deformed to reduce the outside diameter of said assemblies to facilitate insertion and delivery to the implant site. Each electrode assembly is attached to an elongated lead body comprised of a conductor and insulation and adaptable for coupling to an electrical pulse generator.
As mentioned above, compressible member further includes a key structure designed to engage a stiffening member. The stiffening member may be a bladed stylet, for example, having a distal end designed to be inserted within a slot of the compressible member. By rotating the proximal end of the stylet, the at least one electrode of the compressible member may be placed in a predetermined orientation in a vessel.
According to yet another aspect of the invention, an introducer may be provided having an inner lumen to receive the lead when the compressible member is coupled to the stylet. The outer diameter of the introducer is smaller than the compressible member so that when the introducer is slid distally, force asserted by the distal end of the introducer on the compressible member disengages the compressible member from the stylet.
In one embodiment of the invention, lead includes a lumen to receive the stylet. In another embodiment, the lead is coupled to the compressible member in an offset manner such that the longitudinal axis of the lead and the compressible member are not aligned. This allows a proximal end of the style to be located adjacent the lead body while the distal end of the stylet engages the compressible member.
According to one method of using the present invention, a guide catheter is navigated to a desired site of implant. The lead is coupled to stiffening member and loaded into the introducer. The introducer is then used to advance the lead within the lumen of the guide catheter. The introducer is used to deploy the compressible member, which may include rotating the compressible member to orient the electrode in a particular location. If the electrode requires re-positioning, the stylet may be re-inserted into the compressible member. When the electrode is in the desired location, the introducer and stiffening member are withdrawn from the body. Finally, the guide catheter is withdrawn from the body.
According to another method of using the invention, a lead including a lumen is loaded with stiffening member. Then the lead is loaded into the introducer. The introducer is used to push the compressible member to the implant site. The compressible member is deployed, and the introducer and stiffening member are withdrawn from the body.
Other scopes and aspects of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings.